Thread-trimming device on a sewing machine

ABSTRACT

An improved thread cutting device is disclosed for trimming the upper and lower threads in a straight lock stitch sewing machine. The device is positioned at the closest possible position above the rotary hook and is operatable in two different speeds for preparatory and thread-trimming operations, respectively.

' United States Patent Uozaki et al.

[ 1 Nov. 25, 1975 1 THREAD-TRIMMING DEVICE ON A SEWING MACHINE [75]Inventors: Seizo Uozaki, Toyota; Hitoshi Sakashita, Aichi, both of Japan[73] Assignee: Aisin Seiki Kabushiki Kaisha,

Kariya, Japan [221 Filed: May 29, 1974 [21] Appl. No.: 474,462

[30] Foreign Application Priority Data May 30, 1973 Japan 4861376 [52]US. Cl. 112/252 [51] Int. C1. D058 65/02 [58] Field of Search 112/252[56] References Cited UNITED STATES PATENTS 3,141,432 7/1964 Reeber eta1. 112/252 3,173,392 3/1965 Hedegaard 112/252 3,173,393 3/1965 Adam112/252 3,371,633 3/1968 Hedegaard 112/252 3,443,540 5/1969 Hannemarm eta1 112/252 3,756,177 9/1973 Landwehr 112/252 3,776,161 12/1973Papajewski 112/252 Primary ExaminerGeorge l-l. Krizmanich Attorney,Agent, or FirmSughrue, Rothwell, Mion, Zinn & Macpeak 4 Claims, 12Drawing Figures U.S. Patent Nov. 25, 1975 Sheet 1 of3 3,921,554

U.S. Patent Nov. 25, 1975 Sheet 3 of3 3,921,554

THREAD-TRIMMING DEVICE ON A SEWING MAGI-IINE This invention relatesgenerally to industrial straight lock stitch sewing machines. Morespecifically, it relates to improvements in and relating to threadstrimming device.

An object of the present invention is to provide the threads trimmingdevice workable at the best operating phase and at the closest possibleposition to the conventional rotary hook.

A further object of the invention is to provide the threads trimmingdevice of the above kind, adapted for positive prevention of theblowing-out of the upper thread before the catching thereof for thetrimming job.

These and further objects, features and advantages of the invention willbe made more apparent with the following detailed description of theinvention by reference to the accompanying drawings illustrative of apreferred embodiment thereof.

In the drawings:

FIG. 1 is an inverted plan view of essential parts of the thread-cuttingdevice according to the present invention from the bottom side of themachine bed.

FIG. 2 is a perspective view of the essential parts of thethread-cutting device according to the invention.

FIG. 3 is a front elevation of the thread-cutting device when seen fromthe front side of the machine bed which is shown in chaindotted line.

FIG. 4 is a perspective view of a tension release mechanism cooperatingwith the threadcutting device.

FIG. 5 is a partial sectional elevation of a needle bar together with apart of the machine arm, specifically illustrating a timing markprovided on the needle bar.

FIG. 6 is an enlarged detail side view of a pair of partial gearsemployed in the thread-cutting device shown at a timing in coincidenceof that of the needle bar shown in FIG. 5.

FIG. 7 is a partial sectional front view of a thread catcher includedand cooperating with a conventional rotary hook, the scale beingslightly enlarged from that of FIG. 3 and the timing being such that thethread catcher begins to catch the sewing thread.

FIG. 8 is a similar view to FIG. 6, wherein, however, the timing is sameas in FIG. 7.

FIG. 9 is a similar view to FIG. 7, wherein, however, the thread catcherhas caught the sewing yarn.

FIG. 10 is a similar view to FIG. 6, wherein, however, the timingcorresponds to that employed in FIG. 9.

FIG. 11 is a similar view to FIG. 7, wherein, however, the timing issuch that the thread cutter has just cut the thread.

FIG. 12 is a similar view to FIG. 6, wherein, however the timingcorresponds to that employed in FIG. 11.

In the following, a preferred embodiment of the invention will bedescribed in detail by reference to the accompanying drawings.

In FIGS. 1 3, numeral 1 denotes schematically and partly in phantommanner a machine bed, a mounting frame 2 being fixedly attached on alower surface of said bed by means of set screws 3 and 4. A shaft 6having an operating rigid lever portion 5 is mounted rotatably on theframe 2 at 2a and 2b. The shaft 6 is further provided rigidly with anenlarged flange 7 attached thereto by means of a set screw 8. As seen,especially from FIG. 2, the shaft 6 is formed with a shoulder 9 for 2the prevention of occasional axial shift of the shaft, said flange 7serving for the same purpose.

A coil spring 10 is mounted on and between a part of said frame andradial projection 7a of said flange 7. In the case of off-serviceposition of the thread cutter device to be described, said radialprojection 7a is kept in engagement with a stationary stop 11 as shownin FIGS. 1 and 2, said stop being fixedly positioned by being threadedthrough a portion of said frame.

Numeral 12 represents a partial gear toothed only at and mounted looselyon said shaft 6. This partial gear is formed with an axially projectingboss 12a which is formed in turn with an axial slot 14 slidablyreceiving an axial projection 13 projecting rigidly from said flange 7.Partial gear 12 is slidable axially on the shaft 6, but its rotation ismade in unison therewith, by virtue of the fixed mounting of the flange7 on the shaft.

Arm member 15 is mounted loosely on the shaft 6, said member 15 beingformed with a recess 16 kept normally in engagement with the tip end ofa plunger 19 of thread-cutter solenoid 18 which is fixedly mounted on apart of said frame 2 by means of a plurality of set screw 17. Therefore,the arm member 15 can not rotate normally integral with the shaft 6,even if the latter is caused to rotate.

It will be seen from the foregoing that when solenoid 18 is energized bysupply of electric current from a current source, not shown, thereto forthe execution of a thread-cutting job, plunger 19 is caused to advanceleftwards in FIG. 1, so as to push the partial gear 12 and flange 7 inthe same direction against the action of a coil spring 20 providedbetween the last mentioned two members.

Numeral 22 represents a thread-release cable passing through a smallhole formed through one end of said arm member 15 and fixedly attachedthereto by a pair of fixing elements 23 and 23. A flexible cable sheath102 slidably guides the cable 22 and is attached fixedly at its one endto a stationary member 103 by means of a clip 104, said member 103 beingrigid with the solenoid 18.

Numeral 24 represents only partially a conventional hook shaft which issupported rotatably at its one end shown by a bearing 25 press fit inposition into the bed 1 A pivotable holder 26 is provided in closeproximity of the left end of the bearing metal, FIG. 1, but it is prevented from its axial movement by virtue of the provision of stop spring27. The holder 26 and the lever portion 5 are pivotably connected witheach other by a link member 28 and stepped screws 29 and 31).

A stationary cutter blade 32 and a thread guide plate 33 are fixedlyattached to the bed 1 by means of a set screw 31. The cutter blade 32 isarranged in opposition to a thread catcher 35 which is fixedly attachedto the holder 26 by a set screw 34., in such a way that the cutting edge41 formed on the cutter blade and that at 40 formed on thread catch 35can be brought into a shearing relationship for performing athread-cutting job, as will be described later more fully.

The free end portion of thread guide plate 33 has an arc-shape in itsside view, said arc being designed and arranged concentrically with aconventional rotary hook 36. This thread guide plate 33 is arranged tooccupy an intermediate position when seen in the radial direction of therotary hook, as most clearly seen from FIG. 7. The plate 33 is furtherprovided with an opening 97 adapted for passage of the sewing thread soas to keep the part of the latter in coincidence with the center of theneedle.

The thread catcher 35 comprises as its effective portion an arc-shapedportion made concentric to the ro' tary hook and is formed with apointed and portion 37 followed reversedly by a thread-engaging portion38 which is further followed reversedly by a londitudinally groovedportion 39 terminating into a cutting edge 40. This movable cutting edge40 is adapted for cooperating with a cutting edge 41 formed on the tipend of stationary cutting element 32 for performing a thread-cuttingjob, as will be more fully described hereinafter.

Hook shaft 24 is attached fixedly with a driving partial gear 42 bymeans of a set screw 43, said partial gear representing drive teeth at98, as shown in FIGS. 6, 8, l and 12. In succession to these drive teeth98, the partial gear 42 represents on its outer periphery a cam portion92 having a gradually increasing radius of curvature. In furthersuccession to this cam portion 92, the partial gear 42 represents ablank peripheral surface 99 terminating at said teeth 98.

The driving partial gear 42 having the aforementioned structure willrotate only in idle and in unison with the hook shaft 24 during thenormal sewing operation of the machine. However, when the solenoid 18 isenergized for initiating a thread-cutting job, the partial gear 12 iscaused to slide in the aforementioned way so that the latter is broughtinto lateral registration with the companion partial gear 42 adapted forengagement with each other during the rotational movement of hook shaft24.

A tension-release lever 45 and a pivotable member 46 are pivotablymounted on the conventional machine arm 44 by means of a common pivotpin 47, although the set position has been omitted from the drawing. Asshown in FIG. 4, tension release lever 45 is formed with a cam surface48 which is adapted for acting upon a pin or tension stud 49 withrotation of said lever, so as to release the tension of the upper threadat the tension disc unit 50 of the known structure, as in the commonlyknown way.

The cable guide sheath 102 fixedly attached at its one end to the frame2 as shown and described hereinbefore in connection with FIG. 1, has itsopposite end is fixedly attached to the machine arm 44, although notspecifically shown. The cable 22 slidable in and along the sheath 102has its one end fixedly attached to the upper or motion-receiving end ofthe tension release lever 45 as shown in FIG. 4. By the sliding movementof arm member with energization of the solenoid 18 in the aforementionedmanner, the lever 45 is pulled by the cable against the spring action at51 so that the latter is caused to rotate in clockwise about its pivot47 in FIG. 4 for the execution of the tension-releasing job, as wasdescribed hereinbefore. On the contrary, when the solenoid 18 isde-energized, the accumulated energy in the spring 51 is released,thereby the lever 45 is rotated in the counter clockwise direction inFIG. 4 so that the cam surface 48 is disengaged from contact with themotion-receiving end of the pin or stud 49.

When the commonly known lifting plate 52 is lifted by means of kneelifter, as an example, the rotatable member 46 is caused to rotate forpushing a pointed projection of thread tension release lever 45, so asto release upper thread tension, and indeed, by virtue of the fork jointbetween pin 53 and fork 54 of the rotatable member 46.

As shown in FIG. 5, conventional needle bar 94 carrying a needle andreciprocated by a crank mechanism, not shown, by the rotation of aconventional upper or arm shaft, not shown, is given a timing mark shownat 95, being selected at a predetermined position on the needle bar. Inthe present case, when the mark 95 is brought into coincidence with thelower end of needle bar metal 96 as shown, the needle bar will occupy aposition of about 55 degrees in advance of the upper dead point of theneedle bar 94.

As commonly known, the thread tension disc unit 50 is mounted on thefront side of the machine arm in close proximity of the free endextremity of the latter as commonly employed, although not specificallyshown.

The general operation of the thread trimming device so far shown anddescribed is as follows.

When the sewing machine operator operates a manually operable means forstopping the high speed sewing operation, the foot-operated pedal inthis case, is released from its operating position, a clutch isdisengaged from the main drive electric motor and a brake is applied tothe shafting system including, as known, the upper shaft, not shown, fordriving the needle bar 94, and the hook shaft 24, for stopping therotation of these shaft. In this case, the needle bar 94 is brought intoand held just at its lower dead point by actuation of a needleposition-sensing and a source-curre interruption means, not shown, whichare known per se.

When the operator depresses the foot pedal in the reverse direction, anelectric speed slow-down means, not shown, is operated as known per se,and the upper and the lower or hook shaft are caused to rotate at arespective slower constant speed which is selected to l/30 of the highersewing speed. In this way, the needle bar 94 moves upwards from itslower to upper dead point. Before arrival of the needle bar at its upperdead point, a known sensor is brought into operation and the trimmingsolenoid 18 is energized, thereby its plunger 19 being operated to pushthe arm member 15 and partial gear 12 axially in the aforementioned wayfor bringing the partial gear 12 into registration with its companionpartial gear 42 ready for mutual engagement. With rotation of the hookshaft 24 and the needle bar is brought to about 55 degrees, when shownin terms of the crank angle, before its upper dead point, the drivepartial gear 42 is brought into engagement with the follower partialgear 12, thus rotation being transmitted from the former to the latteras shown in FIG. 6. Thus, motion is further transmitted through armmember 7, shaft 6, lever 5 and link 28 to holder 26. This holder beginsto rotate for causing the thread catcher 35 to initiate athread-trimming operation.

Then, two partial gears 12 and 42 take mutually the next timed phaseshown in FIG. 8 wherein the pointed projection 37 of thread catcher 35invades into the loop of upper thread N formed by the rotary hook 36,for catching the thread, as schematically shown in FIG. 7. At the sametime, the thread-engageable portion 38 of thread catcher 35 catches anddraws out the lower thread B extending the bobbin case 91 housed asconventionally within the rotary hook.

At a still further advanced timed phase for the mutually engagingpartial gears 12; 42 as shown in FIG. 10 where they have been completeda partial revolution due to the gear tooth meshing, the upper thread Nis subjected to a upwardly directing drawing action by the conventionalthread take-up lever, not shown. But, in this case, the upper thread isheld by the thread catcher 35 by being engaged thereby, so as to leave aproper end length of the thread, enough for avoiding a slip-out of thethread from the thread eyelet, not shown, of needle 94a replaceablyattached to needle bar 94, at the commencement of the next sewing job.At this stage, the lower thread B, together with a part of the upperthread which lies close to the sewing material, not shown, runs in andalong the groove 39 upon leaving from the thread catcher 35, thus beingprevented from cutting by contact with the cutting edge 41 of stationaryknife 32. Therefore, a proper length of the lower thread as necessaryfor later use upon thread-trimming and reinitiation of a new sewing jobcan be drawn out from the bobbin case 91 and preserved in position.

As the timing of the operational stage shown in FIGS. 9 and 10corresponds to 60 70 in advance of the arrival of the upper dead pointof thread take-up lever, a considerable difficulty will occur by theinvitation of an excess upward pulling of the trimmed upper thread bythe upwardly moving thread take-up lever towards its upper dead point tosuch a degree that the thread slips off the needle, thereby making thenext succeeding sewing operation impossible, if the upper thread shouldhave been trimmed directly after the completion of the aforementionedthread catch operation. On the other hand, if the thread catcher shouldbe moved over a substantial distance after the aforementioned executionthread-catching operation by the latter, it must be necessary toovercome a considerable amount of resistance provided by the part of theupper thread extending from its supply source to the catcher 35 even ifthe thread tension at the tension disc unit 50 has been released. Evenif the upper thread should not have been broken unintentionally in thiscase, the thread-trimming device will require a considerably largeamount of driving force when operating under these conditions. Accordingto the present invention, these otherwise unavoidable conventionaldrawbacks can be substantially obviated.

In the proposed design and arrangement of the thread-trimming deviceaccording to this invention,

such excess drawing-out of the upper thread can effectively avoided bybringing the gear teeth 98; 100 partial gears 12; 42, respectively, intomutual engagement so that the movable cutting edge of the catcher 35 andthe stationary cutting edge 41 of the stationary knife 32 may be broughtrapidly at a highly close distance therebetween directly before thearrival of the specific operational timing stage shown in FIG. 10,thereby bringing the occurrence of a thread-trimming operation as closeas the realization time of the upper dead point of the thread take-uplever. Thence, the drive partial gear 42 will rotate in such a way thatthe cam surface 92 formed in succession to the gear teeth 98 thereonkeeps in sliding contact with the last one of the teeth 93 on thecompanion partial gear 12. By this operation, the cutting edges 40; 41are brought into cooperation with each other, as shown in FIGS. 11 and12, for simultaneous trimming of these threads N and B and until thepractical realization of this trimming job, the thread catcher 35 shiftsat a rather low speed, so as to obviate the aforementioned drawbacks.

Upon execution of the aforementioned thread-trimming job and afterfurther slight rotation of partial gear I 42, the engagement of camsurface 92 of partial gear 42 and the gear tooth group 93 is released.After release of the binding operation by the partial gear 42, thethread catcher 35 will return under the spring force at 10 until its arm7 is brought into contact with stop screw 11 After realization of thisphenomenon, a known position sensor, not shown, will act to sense thebeforehand scheduled upper stop position of the thread take-up leverwhich has been set to a position close to its upper dead point, so as todeliver an electrical instruction signal for the interruption ofelectric current supply to the trimming solenoid 18. In this way,partial gear 12, arm 15 and plunger 19 are caused to return to theirstarting position by the resilient resetting action provided by the coilspring 20.

Under these conditions, therefore, the thread-trimming device is keptineffective and ready for the next trimming operation, even if thesewing machine by caused to run for its regular and renewed sewing job.

At the same time with the pushing movement of the actuated plunger 19upon arm member 15 for the execution of the thread-trimming job, cable22 is also pulled in the aforementioned way, so as to rotate the tensionrelease lever 45, FIG. 4, for pushing the stud 49 towards thread take-updisc unit 50 by means of cam surface 48 on the lever, resulting in thetension release of the thread at the unit. The thread N will bedelivered, therefore, in a smooth manner from its supply source, even ifthe thread take-up lever makes its thread pull-up operation aftersuccessful catch of the upper thread N by the catcher 35, asschematically shown in FIG. 9.

After completion of the thread-trimming job and upon interruption ofcurrent supply to solenoid 18, the tension release lever will be causedto swivel in the opposite or counter clockwise direction in FIG. 4 underthe action of return spring 51, so as to bring the thread take-up discunit into its operating position for tightening the upper thread N.

Next, the operation of the thead guide plate 33 will be describedhereinbelow.

Upon lapse of the timing as represented by FIG. 7, the upper thread Ndrawn-in by rotary hook 36 will be urged to disengage from the latter asa result of the upward pull exerted upon the thread by the thread takeuplever, not shown. As a result, the upper thread may sometimes reep upsubstantially in the peripheral direction of the hook 36 and could beheld far from the pointed projection of the catcher 35 which is nowtrying to catch the thread. As a result, the upper thread could not besubjected to the necessary trimming job at and between the cutting edgesof the stationary and moving cutter knife elements. Or even if trimmed,a shorter length of thread end only could be preserved.

With use of the thread guide plate 33 having an eye opening at 97, theupper thread loop being upwardly pulled by the thread pick-up lever isdrawn-to by the rotary hook 36 only after once passing through thatopening. Therefore, the aforementioned defective large reep-out movementof the: thread in the peripheral direction of hook 36 can be preventedand a guaranteed thread catch may be positively assured.

The trimmed end of the lower thread B is limited by the same opening 97from its free movement, the upper thread N can pick up necessarily thelower thread B at the commencement of the next regular sewing operation.

The embodiments of the invention in which an exclusive property orprivilege is claimed are as follows:

1. A thread-trimming device for an industrial sewing machine,comprising:

a. a first shaft rotatably driven by a main shaft of the machine;

b. first ratchet means disposed upon said first shaft and rotatabletherewith;

c. stationary blade means fixedly secured to the framework of saidmachine;

d. a second shaft disposed parallel to said first shaft;

e. pivotably movable blade means connected to said second shaft;

f. second ratchet means disposed upon said second shaft and beingaxially movable relative thereto so as to selectively engage said firstratchet means; and

g. electrically operated means for moving said second ratchet meansalong said second shaft so as to engage said first ratchet means,whereby said second shaft will be rotated so as to move said movableblade means relative to said stationary blade means to perform thethread trimming operation.

2. A thread-trimming device for an industrial sewing machine accordingto claim 1, wherein said first ratchet means comprises a first partialgear having teeth on only a portion of the periphery thereof and a camsurface successively disposed from said toothed gear portion; and saidsecond ratchet means comprises a second partial gear having teeth ononly a portion of the periphery thereof, whereby upon actuation of saidelectrically operated means, the toothed portions of said first andsecond partial gears are engaged with each other to rapidly rotate saidmovable blade means to an operable position relative to said stationaryblade means and thereafter, said cam surface of said first partial gearportion comes into sliding contact with said second partial gear toslowly rotate said second blade means to cooperate with said first blademeans to thereby perform the thread trimming operation.

3. A thread trimming device according to claim 2, wherein said movableblade means comprises:

a. thread catching means for drawing and catching the lower thread outof a bobbin case of said ma chine for preparing said thread trimmingoperation, and

b. a blade portion for cooperating with said first stationary blademeans to perform said thread trimming operation.

4. A thread trimming device according to claim 3, wherein saidstationary blade means include a thread guide plate secured to saidframework of said machine, said guide plate having a thread guiding holethrough which pass upper and lower threads for assuring said threadtrimming operation and the commencement of the following regular sewingoperation.

1. A thread-trimming device for an industrial sewing machine,comprising: a. a first shaft rotatably driven by a main shaft of themachine; b. first ratchet means disposed upon said first shaft androtatable therewith; c. stationary blade means fixedly secured to theframework of said machine; d. a second shaft disposed parallel to saidfirst shaft; e. pivotably movable blade means connected to said secondshaft; f. second ratchet means disposed upon said second shaft and beingaxially movable relative thereto so as to selectively engage said firstratchet means; and g. electrically operated means for moving said secondratchet means along said second shaft so as to engage said first ratchetmeans, whereby said second shaft will be rotated so as to move saidmovable blade means relative to said stationary blade means to performthe thread trimming operation.
 2. A thread-trimming device for anindustrial sewing machine according to claim 1, wherein said firstratchet means comprises a first partial gear having teeth on only aportion of the periphery thereof and a cam surface successively disposedfrom said toothed gear portion; and said second ratchet means comprisesa second partial gear having teeth on only a portion of the peripherythereof, whereby upon actuation of said electrically operated means, thetoothed portions of said first and second partial gears are engaged witheach other to rapidly rotate said movable blade means to an operableposition relative to said stationary blade means and thereafter, saidcam surface of said first partial gear portion comes into slidingcontact with said second partial gear to slowly rotate said second blademeans to cooperate with said first blade means to thereby perform thethread trimming operation.
 3. A thread trimming device according toclaim 2, wherein said movable blade means comprises: a. thread catchingmeans for drawing and catching the lower thread out of a bobbin case ofsaid machine for preparing said thread trimming operation, and b. ablade portion for cooperating with said first stationary blade means toperform said thread triMming operation.
 4. A thread trimming deviceaccording to claim 3, wherein said stationary blade means include athread guide plate secured to said framework of said machine, said guideplate having a thread guiding hole through which pass upper and lowerthreads for assuring said thread trimming operation and the commencementof the following regular sewing operation.